This invention relates to an offset press having two printing units. More particularly, it is concerned with an offset press comprising a printing unit for ordinary offset printing, and a printing unit including a delivery cylinder positioned adjacent to an impression cylinder in the ordinary offset printing unit, and a number printing cylinder.
In addition to the press of the type mentioned above, there are known two types of presses adapted for both ordinary offset printing and number printing, i.e., one of the type having an impression cylinder for ordinary printing and one of the type including a chain delivery section. These types of presses are different from the first-mentioned type in that a transverse perforation cylinder can be included in the first-mentioned type to enable simultaneous number printing and perforation. An impression cylinder for ordinary printing is not liable to be damaged, as opposed to the type in which another cylinder also serves as an impression cylinder; therefore, no adverse effect is produced on the quality of ordinary printing. It is reliable and efficient in operation, and enables number printing, etc. on the paper held on the impression cylinder. It is an ideal type of press having a number of advantages, including high accuracy of registration.
The conventional press of the type in question has a number printing unit defined by an impression cylinder for ordinary printing, a delivery cylinder, a number printing cylinder and a paper ejection cylinder disposed in that order. If number printing, perforation or resin relief printing is performed, no problem arises, since the printing paper is held against the number printing cylinder. If no number printing or the like is performed, however, the curved trailing edge of the paper rises above the cylinder surface during its travel, and there is every likelihood that the printed surface of the paper may be brought into contact with, and scratched by, objects around the number printing cylinder. This trouble is particularly likely to occur with thick or rigid printing papers which have a greater tendency to curve at the trailing edge.